Such a gear system as mentioned above includes a lubricating oil supply port and a lubricating oil outlet port for use in lubricating and cooling down the gears. The lubricating oil supply port is used for spraying lubricating oil onto the gears, and the lubricating oil outlet port is used for collecting, with an oil scavenging pump, the lubricating oil that has been used for lubricating and cooling down the gears. Power loss in such a gear system is mainly caused by air resistance and lubricating oil agitation resistance, which occur when the gears rotate. Particularly in the case of an aircraft engine, the air resistance is great since the gear train rotates at a relatively high speed. Moreover, in aircrafts developed in recent years, electrification of various airframe facilities has been promoted rapidly. Therefore, in the near future, necessary electric power generation capacity is expected to increase greatly. In this case, power loss in a gear system that is caused by the air resistance and the lubricating oil agitation resistance also increases, which results in an increase in negative influence on the fuel consumption of an aircraft engine such as a jet engine or a gas turbine engine.
For the purpose of reducing the above-described power loss in a gear system, there is a proposed gear shrouding system (see Patent Literature 1) in which a plurality of gears meshing with each other in a gear train are covered by a shroud, so that generation of a swirling air flow of an inverted tornado type, which tends to be generated at the front face of each gear when air is dragged by the front face of each gear due to rotation of the gears, is suppressed and thereby the air resistance is reduced. The shroud includes: a pair of side walls disposed opposite the sides of each gear and adjacent to the outer diameter surface of each gear; and an end wall disposed perpendicular to the pair of side walls and being disposed parallel to the front face of each gear, such that the side walls and the end wall enclose the front face of each of the plurality of gears of the gear train. The end wall is provided with a first port for injecting lubricating oil onto the gears and a second port for discharging the lubricating oil from the shroud. The shrouding system is disposed in close proximity to the teeth of the gears, and thereby suppresses the generation of the above-described swirling air flow at the front face of each gear and reduces the air resistance.